source: git/kernel/preimage.cc @ fbc7cb

jengelh-datetimespielwiese
Last change on this file since fbc7cb was a9c298, checked in by Hans Schoenemann <hannes@…>, 9 years ago
format stuff
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File size: 4.3 KB
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1#ifdef HAVE_CONFIG_H
2#include "singularconfig.h"
3#endif /* HAVE_CONFIG_H */
4#include "mod2.h"
5
6#include <omalloc/omalloc.h>
7#include <misc/auxiliary.h>
8#include <misc/options.h>
9#include <misc/intvec.h>
10
11#include <kernel/polys.h>
12#include <polys/monomials/ring.h>
13
14
15#include <kernel/febase.h>
16#include <kernel/ideals.h>
17#include <kernel/kstd1.h>
18#include <kernel/khstd.h>
19
20#include <kernel/kutil.h>
21
22
23#ifdef HAVE_PLURAL
24#include <polys/nc/nc.h>
25#endif
26
27/*2
28*shifts the variables between minvar and maxvar of p  \in p_ring to the
29*first maxvar-minvar+1 variables in the actual ring
30*be carefull: there is no range check for the variables of p
31*/
32static poly pChangeSizeOfPoly(ring p_ring, poly p,int minvar,int maxvar, const ring dst_r)
33{
34  int i;
35  poly result = NULL,resultWorkP;
36  number n;
37
38  if (p==NULL) return result;
39  else result = p_Init(dst_r);
40  resultWorkP = result;
41  while (p!=NULL)
42  {
43    for (i=minvar;i<=maxvar;i++)
44      p_SetExp(resultWorkP,i-minvar+1,p_GetExp(p,i,p_ring),dst_r);
45    p_SetComp(resultWorkP,p_GetComp(p,p_ring),dst_r);
46    n=n_Copy(pGetCoeff(p),dst_r->cf);
47    p_SetCoeff(resultWorkP,n,dst_r);
48    p_Setm(resultWorkP,dst_r);
49    pIter(p);
50    if (p!=NULL)
51    {
52      pNext(resultWorkP) = p_Init(dst_r);
53      pIter(resultWorkP);
54    }
55  }
56  return result;
57}
58
59
60
61/*2
62*returns the preimage of id under theMap,
63*if id is empty or zero the kernel is computed
64* (assumes) that both ring have the same coeff.field
65*/
66ideal maGetPreimage(ring theImageRing, map theMap, ideal id, const ring dst_r)
67{
68  ring sourcering = dst_r;
69
70#ifdef HAVE_PLURAL
71  if (rIsPluralRing(theImageRing))
72  {
73    if ((rIsPluralRing(sourcering)) && (ncRingType(sourcering)!=nc_comm))
74    {
75      Werror("Sorry, not yet implemented for noncomm. rings");
76      return NULL;
77    }
78  }
79#endif
80
81  int i,j;
82  poly p,/*pp,*/q;
83  ideal temp1;
84  ideal temp2;
85
86  int imagepvariables = rVar(theImageRing);
87  int N = rVar(dst_r)+imagepvariables;
88
89  ring tmpR;
90  if (rSumInternal(theImageRing,sourcering,tmpR,FALSE,TRUE)!=1)
91  {
92     WerrorS("error in rSumInternal");
93     return NULL;
94  }
95
96  assume(n_SetMap(theImageRing->cf, dst_r->cf) == ndCopyMap);
97
98  if (theImageRing->cf != dst_r->cf)
99  {
100    /// TODO: there might be extreme cases where this doesn't hold...
101    Werror("Coefficient fields/rings must be equal");
102    return NULL;
103  }
104
105  const ring save_ring = currRing; if (currRing!=tmpR) rChangeCurrRing(tmpR); // due to kStd
106
107  if (id==NULL)
108    j = 0;
109  else
110    j = IDELEMS(id);
111  int j0=j;
112  if (theImageRing->qideal!=NULL) j+=IDELEMS(theImageRing->qideal);
113  temp1 = idInit(sourcering->N+j,1);
114  for (i=0;i<sourcering->N;i++)
115  {
116    q = p_ISet(-1,tmpR);
117    p_SetExp(q,i+1+imagepvariables,1,tmpR);
118    p_Setm(q,tmpR);
119    if ((i<IDELEMS(theMap)) && (theMap->m[i]!=NULL))
120    {
121      p = p_SortMerge(
122                      pChangeSizeOfPoly(theImageRing, theMap->m[i], 1, imagepvariables, tmpR),
123                      tmpR);
124      p=p_Add_q(p,q,tmpR);
125    }
126    else
127    {
128      p = q;
129    }
130    temp1->m[i] = p;
131  }
132  id_Test(temp1, tmpR);
133  for (i=sourcering->N;i<sourcering->N+j0;i++)
134  {
135    temp1->m[i] = p_SortMerge(
136                              pChangeSizeOfPoly(theImageRing, id->m[i-sourcering->N], 1, imagepvariables, tmpR),
137                              tmpR);
138  }
139  for (i=sourcering->N+j0;i<sourcering->N+j;i++)
140  {
141    temp1->m[i] = p_SortMerge(
142                              pChangeSizeOfPoly(theImageRing, theImageRing->qideal->m[i-sourcering->N-j0], 1, imagepvariables, tmpR),
143                              tmpR);
144  }
145  // we ignore here homogenity - may be changed later:
146
147  temp2 = kStd(temp1,NULL,isNotHomog,NULL);
148
149  id_Delete(&temp1,tmpR);
150  for (i=0;i<IDELEMS(temp2);i++)
151  {
152    if (p_LowVar(temp2->m[i], currRing)<imagepvariables) p_Delete(&(temp2->m[i]),tmpR);
153  }
154
155  // let's get back to the original ring
156  //rChangeCurrRing(sourcering);
157  temp1 = idInit(5,1);
158  j = 0;
159  for (i=0;i<IDELEMS(temp2);i++)
160  {
161    p = temp2->m[i];
162    if (p!=NULL)
163    {
164      q = p_SortMerge(
165                      pChangeSizeOfPoly(tmpR, p, imagepvariables+1, N, sourcering),
166                      sourcering);
167      if (j>=IDELEMS(temp1))
168      {
169        pEnlargeSet(&(temp1->m),IDELEMS(temp1),5);
170        IDELEMS(temp1)+=5;
171      }
172      temp1->m[j] = q;
173      j++;
174    }
175  }
176  id_Delete(&temp2, tmpR);
177  idSkipZeroes(temp1);
178
179  if (currRing!=save_ring) rChangeCurrRing(save_ring);
180
181  rDelete(tmpR);
182  return temp1;
183}
184
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